I think there will be variable experiences with this issue. The line lengths will vary with printer drivers for instance. Then you can do things on the second last line such as delete 'the' or 'of' to get the 6.4% to fall at the end of the line. In one case it sits out and the other it aligns
I really have no idea how the justification is calculated but it appears to squeeze content that almost fits as well as stretching content that is a little short. Perhaps when it is squeezes a line these outriders happen but they don't if the line requires expansion.
The Justify Low setting 'appears' to work in this paragraph but I would want to see a large number of instances and vary margin sizes, typefaces and font sizes before I would be fully confident in saying that is the solution.